﻿using System;
using System.Reflection;
using System.Reflection.Emit;

/*
 *  author: able
 *  @2012/2/25 23:39:13
 * 
 */
namespace __ts.Core.Util
{
    public class FastMethodInvoker<TInvoked, TReturn>
    {
        #region Fields

        private delegate TReturn FastInvokeHandler(TInvoked target, params object[] paramters);
        private FastInvokeHandler _fastInvokeHandler;

        #endregion

        #region Methods

        public FastMethodInvoker(string method)
        {
            _fastInvokeHandler = GetMethodInvoker(typeof(TInvoked).GetMethod(method));
        }

        public TReturn Invoke(TInvoked target, params object[] paramters)
        {
            return _fastInvokeHandler.Invoke(target, paramters);
        }

        public IAsyncResult BeginInvoke(TInvoked target, object[] paramters, AsyncCallback callback, object @object)
        {
            return _fastInvokeHandler.BeginInvoke(target, paramters, callback, @object);
        }

        private FastInvokeHandler GetMethodInvoker(MethodInfo method)
        {
            DynamicMethod dynamicMethod = new DynamicMethod(string.Empty,
                typeof(TReturn), new Type[] { typeof(TInvoked), typeof(object[]) }, method.DeclaringType.Module);


            ILGenerator il = dynamicMethod.GetILGenerator();
            ParameterInfo[] ps = method.GetParameters();
            Type[] paramTypes = new Type[ps.Length];
            for (int i = 0; i < paramTypes.Length; i++)
            {
                if (ps[i].ParameterType.IsByRef)
                    paramTypes[i] = ps[i].ParameterType.GetElementType();
                else
                    paramTypes[i] = ps[i].ParameterType;
            }
            LocalBuilder[] locals = new LocalBuilder[paramTypes.Length];

            for (int i = 0; i < paramTypes.Length; i++)
                locals[i] = il.DeclareLocal(paramTypes[i], true);

            for (int i = 0; i < paramTypes.Length; i++)
            {
                il.Emit(OpCodes.Ldarg_1);
                EmitFastInt(il, i);
                il.Emit(OpCodes.Ldelem_Ref);
                EmitCastToReference(il, paramTypes[i]);
                il.Emit(OpCodes.Stloc, locals[i]);
            }

            if (!method.IsStatic)
                il.Emit(OpCodes.Ldarg_0);

            for (int i = 0; i < paramTypes.Length; i++)
            {
                if (ps[i].ParameterType.IsByRef)
                    il.Emit(OpCodes.Ldloca_S, locals[i]);
                else
                    il.Emit(OpCodes.Ldloc, locals[i]);
            }

            if (method.IsStatic)
                il.EmitCall(OpCodes.Call, method, null);
            else
                il.EmitCall(OpCodes.Callvirt, method, null);

            if (method.ReturnType == typeof(void))
                il.Emit(OpCodes.Ldnull);
            else
                EmitBoxIfNeeded(il, method.ReturnType);

            for (int i = 0; i < paramTypes.Length; i++)
            {
                if (ps[i].ParameterType.IsByRef)
                {
                    il.Emit(OpCodes.Ldarg_1);
                    EmitFastInt(il, i);
                    il.Emit(OpCodes.Ldloc, locals[i]);
                    if (locals[i].LocalType.IsValueType)
                        il.Emit(OpCodes.Box, locals[i].LocalType);
                    il.Emit(OpCodes.Stelem_Ref);
                }
            }

            il.Emit(OpCodes.Ret);
            FastInvokeHandler invoker = (FastInvokeHandler)dynamicMethod.CreateDelegate(typeof(FastInvokeHandler));
            return invoker;
        }

        private void EmitCastToReference(ILGenerator il, Type type)
        {
            if (type.IsValueType)
            {
                il.Emit(OpCodes.Unbox_Any, type);
            }
            else
            {
                il.Emit(OpCodes.Castclass, type);
            }
        }

        private void EmitBoxIfNeeded(ILGenerator il, Type type)
        {
            if (type.IsValueType)
            {
                il.Emit(OpCodes.Box, type);
            }
        }

        private void EmitFastInt(ILGenerator il, int value)
        {
            switch (value)
            {
                case -1:
                    il.Emit(OpCodes.Ldc_I4_M1);
                    return;
                case 0:
                    il.Emit(OpCodes.Ldc_I4_0);
                    return;
                case 1:
                    il.Emit(OpCodes.Ldc_I4_1);
                    return;
                case 2:
                    il.Emit(OpCodes.Ldc_I4_2);
                    return;
                case 3:
                    il.Emit(OpCodes.Ldc_I4_3);
                    return;
                case 4:
                    il.Emit(OpCodes.Ldc_I4_4);
                    return;
                case 5:
                    il.Emit(OpCodes.Ldc_I4_5);
                    return;
                case 6:
                    il.Emit(OpCodes.Ldc_I4_6);
                    return;
                case 7:
                    il.Emit(OpCodes.Ldc_I4_7);
                    return;
                case 8:
                    il.Emit(OpCodes.Ldc_I4_8);
                    return;
            }

            if (value > -129 && value < 128)
            {
                il.Emit(OpCodes.Ldc_I4_S, (SByte)value);
            }
            else
            {
                il.Emit(OpCodes.Ldc_I4, value);
            }
        }

        #endregion
    }
}
